She joined the band on stage to sing “Ordinary Love,” which was originally featured in the 2013 film, Mandela: Long Walk To Freedom. Gaga sung it as a duet with Bono, and rocked out behind the piano. “ ‘Ordinary Love,’ an extraordinary girl, Lady Gaga!” Bono said after they finished.

Gaga is just one of the many celebrity guest stars who dropped by U2’s week of New York...